Method for implanting a laminoplasty

ABSTRACT

A medical implant device for use in spinal surgery, and more preferably for use in laminoplasty surgery is provided. The implant is a cage-like member having a generally hollow, elongate body with open ends. The implant is formed from a generally hollow, elongate body having four sides: opposed cephalad and caudal sides, and opposed posterior and anterior sides adjacent to the cephalad and caudal sides. The four sides extend along a longitudinal axis, and define an inner lumen extending between opposed first and second open ends.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/260,329,filed Sep. 30, 2002, now U.S. Pat. No. 6,712,852 entitled “LaminoplastyCage,” which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to spinal implant device, and moreparticularly to spinal cages useful in laminoplasty surgery.

BACKGROUND OF THE INVENTION

Spinal stenosis is the narrowing of the spinal cord canal, and canresult in pain, weakness in arms and/or legs, and unsteadiness in thegait. For mild conditions, conservative treatment may be sufficient.When symptoms are severe or progressive, however, cervical laminoplastysurgery may be required to enlarge the spinal canal to relievecompression of the spinal cord. Common indications which give rise to aneed for laminoplasty surgery include stenosis of the spinal canal,ossification of the posterior longitudinal ligament (OPLL), andspondylotic myelopathy.

Surgical techniques used to perform laminoplasty surgery can vary andwill depend on many factors, including the source of the spinal cordcompression, the number of vertebral segments involved in the diseaseprocess, and the cervical alignment. Two common surgical laminoplastytechniques include open door laminoplasty and midline splittinglaminoplasty. In open door laminoplasty, the lamina is cut on one sideand hinged on the other side. The lamina is then rotated to open thecanal, and sutures are placed on the hinged side to maintain theopening. Eventually, bone growth will fill in the gap created on the cutside. In midline splitting laminoplasty, both sides of the lamina arehinged, and the spinous process is bisected into two halves. Both halvesare then rotated outwards, and a strut graft is placed between thehalves to secure the opening.

Several devices exists for maintaining or stabilizing the lamina in theopen or split position. U.S. Pat. No. 6,080,157 of Cathro et al., forexample, discloses a device for stabilizing the lamina after open doorlaminoplasty surgery. The device includes a spacer which is shaped toengage between severed edges of a lamina, and a retainer attached to thespacer which is adapted to maintain the spacer in an operative position.U.S. Pat. No. 6,358,254 of Anderson also discloses a device forexpanding the spinal canal. The device includes two stents, two washers,two screws, and a cable. In use, pedicle cuts are made in the vertebra,and a screw is then inserted into each cut, through a washer and astent, to expand the cut bone. The cable is then attached to each washerand strapped around the posterior portion of the vertebrae to stabilizethe expanded canal and allow the vertebrae to heal with the spinal canalexpanded.

While these devices have proven effective, they can be difficult toimplant, resulting in increased medical costs. Moreover, the devices donot have a substantially low-profile, and thus can potentially causedamage to surrounding tissue and/or to the spinal cord. The devices arealso not designed to restore the natural dynamics of the cervical spine,and thus can cause discomfort to the patient.

Accordingly, there exists a need for an improved laminoplasty implantthat is effective to maintain and stabilize the position of the laminaafter laminoplasty surgery. Moreover, there is a need for a device thatcan be easily and safely implanted, that will allow for permanent bonyincorporation when used with bone growth promoting materials, that willallow for muscle re-attachment, and that will restore the naturaldynamics of the cervical spine.

SUMMARY OF THE INVENTION

The present invention provides a medical implant device having a hollowelongate body including a longitudinal axis, opposed cephalad and caudalsides, and opposed posterior and anterior sides adjacent to the cephaladand caudal sides. The cephalad, caudal, posterior, and anterior sidesdefine an inner lumen having opposed first and second open ends. Theimplant can be used for a variety of applications, but is preferablyused to stabilize and maintain the position of a bisected spinousprocess after laminoplasty surgery.

In one embodiment, at least one of the cephalad side, the caudal side,and the posterior side includes at least one perforation formed therein,and the anterior side of the body is perforation-free. Preferably, thecephalad side, the caudal side, and the posterior side each include aseveral perforations formed therein. The perforations can have a varietyof shapes and size, but are preferably elongated slots extending in adirection transverse to the longitudinal axis of the of the elongatebody. The slots can optionally include a suture-receiving recess formedtherein for retaining suture.

In another embodiment, the anterior side of the implant includes a firstedge mated to the cephalad side and a second edge mated to the caudalside. Preferably, the first and second edges of the anterior side aresubstantially rounded. The anterior side of the elongate body can alsobe curved along the longitudinal axis such that an outer surface of theanterior side is concave. The rounded edges and the curved anterior sideprevent potential abrasion or damage to tissue surrounding the implant,and provide additional space for the spinal cord in the spinal canal.The entire elongate body can also be curved along the longitudinal axissuch that an outer surface of the anterior side is concave, and an outersurface of the posterior side is convex. That is, the planes defined bythe first and second open ends are converging. This can be effected bydesigning the elongate body with the posterior side being longer thanthe anterior side.

In another embodiment, the elongate body preferably has an anatomicalcross-section extending in a direction transverse to the longitudinalaxis, such that the cross-section of the elongate body conforms to theshape of a patient's bisected spinous process. By way of non-limitingexample, the cross-section can be in the shape of a parallelogram, asquare, a rectangle, a diamond, an oval, and a circle. The first andsecond open ends of the elongate body can also have an anatomical shapesuch that they are adapted to be positioned between a split spinousprocess of a patient's spinal system. Preferably, the first and secondopen ends are angled with respect to the longitudinal axis.

In another embodiment, the elongate body includes first and secondhalves positioned on opposed sides of a midpoint of the body. The firstand second halves are preferably angled with respect to one another,such that the implant is bent at the midpoint. The bend is effective toprovide additional space for the spinal cord within the spinal canal.

In other aspects of the invention, the implant can include a spinousprocess replacement member extending outward from the body in adirection transverse to the longitudinal axis. In another embodiment,the implant can include at least one radiopaque member disposed thereinand configured to provide an x-ray visible reference to indicate theposition of the implant with respect to an anatomical structure when theimplant is positioned within an interstitial space.

In yet another embodiment of the present invention, a medical implantdevice is provided having a hollow elongate body including alongitudinal axis, opposed cephalad and caudal sides, and opposedposterior and anterior sides adjacent to the cephalad and caudal sides.The cephalad side, caudal side, posterior side, and anterior side definean inner lumen having opposed first and second open ends. The implantfurther includes a fixation element receiving member mated to theposterior side of the implant, adjacent the first open end. The fixationelement receiving member extends at an angle with respect to thelongitudinal axis and is effective to receive a fixation element forattaching the implant to a bone structure.

In other aspects, the posterior and anterior sides of the implant have alength extending along the longitudinal axis greater than a length ofthe cephalad and caudal sides, and the cephalad and caudal sides eachinclude a concave recess formed adjacent each of the first and secondends, such that the first and second ends are adapted to seat a bonestructure. The anterior side of the implant, adjacent the first openend, can also include an extension member opposed to the fixationelement receiving member.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is an anterior-cephalad perspective view of an implant accordingto one embodiment of the present invention;

FIG. 2 is an end view of the implant shown in FIG. 1;

FIG. 3 is a cephalad side view of the implant shown in FIG. I having aspinous process replacement member;

FIG. 4 is posterior-cephalad perspective view of another embodiment ofan implant according to the present invention;

FIG. 5 is perspective view of an implant according to the presentinvention positioned in a patient's spinal column after laminoplastysurgery;

FIG. 6 is a cephalad side view of another embodiment of an implanthaving a fixation element receiving member;

FIG. 7 is an end view of the implant of FIG. 6; and

FIG. 8 is an illustration showing the implant of FIG. 6 positionedwithin a bisected vertebra.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a medical implant device for use inspinal surgery, and more preferably for use in laminoplasty surgery. Theimplant is a cage-like member having a generally hollow, elongate bodywith open ends. The implant can be adapted for use in a variety ofapplications, but is preferably used to maintain the position ofvertebra after midline or open door laminoplasty surgery. The implant isparticularly advantageous in that it is easy to implant, it will allowfor permanent bony incorporation when used with bone growth promotingmaterials, it will allow for muscle re-attachment, it will restore thenatural dynamics of the cervical spine, and it has a substantiallylow-profile to avoid or prevent damage to surrounding tissue.

FIGS. 1 and 2 illustrate one embodiment of an implant 10 according tothe present invention. The implant 10 can have a variety of shapes andsizes, but preferably has a size and a geometry that enables it to bepositioned in a bisected spinous process, and to remain securelypositioned until healing and fusion take place. Moreover, the implant 10preferably has a substantially low profile to prevent potential abrasionor damage to surrounding tissue. As shown in FIG. 1, the implant 10 isformed from a generally hollow, elongate body having four sides: opposedcephalad and caudal sides 12, 14, and opposed posterior and anteriorsides 16, 18 adjacent to the cephalad and caudal sides 12, 14. Theimplant 10 has a longitudinal axis L and the four sides 12, 14, 16, 18define an inner lumen 23 (FIG. 2) extending between opposed first andsecond open ends 22, 24. The sides 12, 14, 16, 18 of the implant 10 canbe substantially planar, or can be curved along the longitudinal axis Ldepending on the intended use. As shown in FIG. 1, the implant 10 iscurved along the longitudinal axis L toward the anterior side 18, suchthat the outer surface of the anterior side 18 has a concave shape.Since the anterior side 18 is adapted to face a patient's spinal cordwhen implanted, the curved shape of the implant 10 will provideadditional clearance for the spinal cord. A person having ordinary skillin the art will appreciate that the shape of each side 12, 14, 16, 18can vary, and that all four sides 12, 14, 16, 18 can have differentconfigurations.

The implant 10 can also have a variety of cross-sectional shapesextending in a direction transverse to the longitudinal axis. By way ofnon-limiting example, the cross-section can be in the shape of a square,a rectangular, a circle, an oval, a diamond, and a triangle. Preferably,the implant has a cross-section that is adapted to contour the shape ofa bisected spinous process. FIG. 2 illustrates an end view of implant 10have a cross-section in the shape of a parallelogram. As shown, thecaudal side 12 has a width w₁ greater than a width w₂ of the cephaladside 14, such that the height h_(i) of the implant 10 between theposterior and anterior sides 16, 18 increases from the cephalad side 14to the caudal side 12. The anatomical shape of the implant reducesimpingement with adjacent bone structures and grafts, facilitates thesecure positioning of the implant, and increases the patient's range ofmotion. The open ends 22, 24 of the implant 10 are also preferablyadapted to contour the shape of a bisected spinous process. Preferably,each end 22, 24 is angled to match the angle of the cut ends of thebisected spinous process. That is, the planes defined by the first andsecond open ends 22, 24 are converging. This can be effected bydesigning the elongate body with the posterior side 16 being longer thanthe anterior side 18.

The implant 10 can also be adapted to prevent potential abrasion ordamage to surrounding tissue. Still referring to FIGS. 1 and 2, theimplant 10 includes four edges 28, 30, 32, 34 extending between eachside 12, 14, 16, 18. The first edge is positioned between the anteriorside 18 and the caudal side 12, and the second edge is positionedbetween the anterior side 18 and the cephalad side 14. The first andsecond edges 28, 30 are preferably substantially rounded to preventpotential abrasion or damage to the spinal cord and tissue surroundingthe implant 10. The third and fourth edges 32, 34, which are positionedbetween the posterior side 16 and the caudal side 12, and the posteriorside 16 and the cephalad side 14, respectively, can have any shape, asthey are not positioned adjacent the spinal cord when implanted.Preferably, the third and fourth edges 32, 34 have a slightly roundedprofile.

The dimensions of the implant 10 can also vary depending on the intendeduse. Preferably, the implant 10 has a length l_(i) (FIG. 1), width w_(i)(FIG. 2), and height h_(i) (FIG. 2) that is sufficient to fit within abisected spinous process and to provide the necessary expansion of thespinal canal. More preferably, the implant 10 has a length l_(i)extending between the first and second open ends 22, 24 that is in therange of about 8 mm to 25 mm, a height h_(i) extending between theposterior and anterior sides 16, 18 that is in the range of about 4 mmto 10 mm, and a width w_(i) extending between the caudal and cephaladsides 12, 14 that is in the range of about 5 mm to 15 mm. A personhaving ordinary skill in the art will appreciate that the dimensions ofthe implant can vary depending on the intended use.

Referring back to FIG. 1, the implant 10 can also include one or moreperforations 26 formed therein for facilitating secure placement andfusion of the implant 10 within the split spinous process. Theperforations 26 can have any shape and size, and can be formed in one ormore of the sides 12, 14, 16, 18, of the implant 10. Preferably, theanterior side of the implant 18 is perforation-free to prevent potentialabrasion or other damage to the dura mater, and the remaining threesides 12, 14, 16 each preferably include one or more perforations 26formed therein. While the size, shape, and placement of each perforation26 can vary, the perforations 26 are preferably in the form of elongatedslots extending in a direction transverse to the longitudinal axis L ofthe implant 10. Each slot 26 should have a size and shape sufficient toallow for vascularization of the implant, the placement of bone growthpromoting materials inside the implant, as well as muscle re-attachmentto the bone growth promoting materials. In an exemplary embodiment,shown in FIG. 4, at least one of the slots 126 formed in the implant 100can include a suture-receiving recess 127. The recess 127 is effectiveto receive sutures used to secure the implant 100 to surrounding bone,and to prevent the sutures from sliding within the slot 126. A personhaving ordinary skill in the art will appreciate that a variety oftechniques can be used to secure suture to the implant, and to securethe implant to the adjacent bone structure.

FIG. 3 illustrates another embodiment of the implant 10 shown in FIG. 1having a spinous process replacement member 42. The replacement member42 is effective to allow for muscle re-attachment and will restore thenatural dynamics of the cervical spine. The replacement member 42 canhave a variety of configurations, but should conform to the naturalshape of the spinous process. Preferably, the replacement member 42 ispreferably a rigid elongate member that extends outward from the implantin a direction transverse to the longitudinal axis L. The replacementmember 42 should be mated to or disposed on the posterior side 16 of theimplant 10, and should be positioned at a midpoint m, shown along linem-m. The replacement member 42 can be solid or hollow, and canoptionally include one or more perforations (not shown) formed therein.

The replacement member 42 can be permanently or removably attached tothe implant 10. Where the implant 10 is removably attached, thereplacement member 42 can be mated to the posterior side 16 of theimplant 10 using any type of fastening element, such as, for example,threads which engage similar threads formed on a bore extending into theposterior side 16 of the implant 10, or a taper post matable with ataper bore disposed in the posterior side 16. A person having ordinaryskill in the art will readily appreciate that the replacement member 42can be disposed on or attached to the implant 10 using a variety ofdifferent techniques.

FIG. 4 illustrates another embodiment of an implant 100 having opposedcaudal and cephalad sides 112, 114, and opposed posterior and anteriorsides 116, 118 adjacent the caudal and cephalad sides 112, 114. Theimplant 100 is similar to implant 10, but includes a bend 143 formed ata midpoint M, shown as line M-M. The bend 143 is directed toward theanterior side 118 of the implant, such that the two halves of theanterior side 118, extending from the midpoint M, are bent toward oneanother. As a result, the implant includes two longitudinal axis L₁, L₂extending from the midpoint M. The angle α of the bend 143, measured atthe anterior side 143, can vary depending on the intended use, butpreferably the bend 143 has an angle a in the range of about 150° to170°. In use, the bend 143 is effective to provide additional space forthe spinal cord. More preferably, the bend 143 provides about 0.5 mm to2.5 mm more space for the spinal cord.

FIG. 5 illustrates an implant 200, representative of an implantaccording to the present invention, disposed within a bisected spinousprocess 206 of a vertebra 204 in a patient's spinal column. The spinousprocess 206 is prepared by forming a cut through the bone to separatethe spinous process 206 into two halves. A small incision 201 is thenformed on each side of the spinous process 206 between spinous articularprocess 207 and the transverse process 208. The incision 201 iseffective to form a hinge to allow the bisected spinous process 206 tobe opened. The implant 200 is then positioned between the bisectedspinous process 206, thereby enlargening the spinal canal to relievecompression on the spinal cord 210. A person having ordinary skill inthe art will appreciate that a variety of techniques can be used forsecuring the implant 200 to the adjacent bone.

By way of non-limiting example, the implant 200 can be secured in placeusing sutures or other securing techniques known in the art. Preferably,as shown in FIG. 5, a suture 209 is inserted through one side of thebisected spinous process 206, through the inner lumen of the implant200, and then through the other side of the bisected spinous process206. The suture 209 is then tied to prevent movement of the implant 200with respect to the vertebra 204. The implant can also optionallyinclude bone growth promoting materials disposed therein for promotingfusion of the implant to the spinous process. Preferably, the innerlumen of the implant is packed with morsellized bone graft.

In order to facilitate placement of an implant in a split spinousprocess, the implant can optionally include one or more radiopaquemarkers disposed therein. The radiopaque markers are configured toprovide an x-ray visible reference to indicate the position of theimplant with respect to an anatomical structure when the implant ispositioned within an interstitial space. The markers can have virtuallyany configuration, and can be positioned around and/or within theimplant. The position of the markers should be adapted to facilitateaccurate placement of the implant in the split spinous process.Referring back to FIG. 2, the implant 10 is shown having markers 40 aand 40 b extending along edges 32 and 34. The markers 40 a, 40 b areeach in the form of an elongate wire, and are disposed within the bodyof the implant 10. Preferably, the body of the implant 10 is formed froma radiolucent material to allow the radiopaque markers to bedistinguished from the implant 10 in an x-ray image.

FIGS. 6 and 7 illustrate another embodiment of an implant 300 preferablyfor use in open-door laminoplasty surgery. The implant 300 is similar toimplant 10 shown in FIG. 1 and includes opposed cephalad and caudalsides 312, 314, and opposed posterior and anterior sides 316, 318adjacent to the cephalad and caudal sides 312, 314. The four sides 312,314, 316, 318 extend along a longitudinal axis L, and define an innerlumen 323 (FIG. 7) extending between opposed first and second open ends322, 324. While the implant 300 is shown having an inner lumen 323formed therein, the implant 300 can alternatively be a solid, elongatemember.

The implant 300 can have a variety of shapes and sizes, and can besubstantially planar, curved, or bent. Preferably, the caudal, cephalad,posterior, and anterior sides 314, 314, 316, 318 are substantiallyplanar and form a rectangular or substantially square elongate member.The posterior and anterior sides 316, 318 can have a length l_(a)greater than a length l_(b) of the caudal and cephalad sides 312, 314.The difference in length is effective to form a concave recess 340 ineach open end 322, 324 of the implant 300. In use, the concave recess340 is adapted to seat, and optionally engage and/or conform to, aportion of a bone structure to facilitate the secure placement of theimplant 300 between the bisected bone structure. The implant 300 canalso optionally include one or more perforations 326, similar toperforations 26 disclosed above with reference to FIG. 1, formed in oneor more sides 312,314, 316,318 of the implant 300. Preferably, theperforations 326 are formed in the caudal, cephalad, and posterior sides312, 314, 316, and the anterior side 318 is perforation-free to protectthe spinal cord.

The implant 300 can also include a fixation element receiving member 336mated to the posterior side 316 of the implant 300 that is effective toreceive a fixation element, such as a bone screw 330 or a suturematerial, for attaching the implant 300 to a bone structure. Thereceiving member 336 can have a variety of configurations, but ispreferably an extension of the posterior side 316. The receiving member336 can have a substantially planar shape, can be angled, or can havesome other shape. While FIGS. 6 and 7 illustrate the receiving member336 formed adjacent the first open end 322, the receiving member 336 canbe formed on either one or both of the first and second ends 322, 324.Preferably, the receiving member 336 is disposed at an angle α′ withrespect to the longitudinal axis. The angle α′ can vary depending on theintended use, but preferably the receiving member 336 extends from theposterior side 316 in the posterior direction at an angle α′, relativeto the longitudinal axis, in the range of about 35° to 75°, as measuredin a direction toward the first open end 322.

The receiving member 336 can include a bore 337 formed therein forreceiving a fixation element. By way of non-limiting example, FIGS. 6and 7 illustrate bone screw 330 disposed within the bore 337 in thereceiving member 336. The bone screw 330 includes a head 332 positionedon one side of the bore 337, and a shank 334 disposed through the bore337. The shank 334 includes threads formed thereon for threading thebone screw 330 into a bone structure. A person having ordinary skill inthe art will appreciate that a variety of fixation elements can be usedwith the implant 300.

The implant 300 can also include an extension member 328 formed on theanterior side 318 adjacent the first open end 322, and opposed to thereceiving member 336. The extension member 328 can also be substantiallyplanar, or can be positioned at an angle with respect to thelongitudinal axis L in a direction opposed to the receiving member 336.The extension member 338 is effective to facilitate the secure placementof the implant 300 between a bisected bone structure. More particularly,the extension member 338 should be sufficient to prevent the implant 300from becoming dislodged during insertion of the fixation element 330into the bone structure.

FIG. 8 illustrates the implant 300 in use disposed within a vertebra 360of a patient's spinal column. The implant 300 is positioned between abisected lamina 354 of the vertebra 360, thereby enlarging the spinalcanal 331. The fixation device, e.g., the bone screw 330, is disposedthrough the bore formed in the receiving member 336 and threaded intothe lamina 354 to secure the position of the implant 300 with respect tothe vertebra 360.

While not illustrated, an implant according to the present invention caninclude a variety of other features to facilitate placement of theimplant in the split spinous process or lamina. By way of non-limitingexample, the implant can include a number of bone engaging surfacefeatures formed on the end surfaces. The bone engaging surface featuresare preferably adapted to engage the cut portion of the split spinousprocess or lamina to facilitate the secure placement of the implant. Inanother embodiment, the implant can be adapted to mate to an insertiontool for inserting the implant into the split spinous process. Forexample, the implant can be used in conjunction with a distractor orspreader device. A person having ordinary skill in the art willappreciate that a variety of insertion tools can be used with theimplant of the present invention, and that the implant can be modifiedto work with such a tool.

The materials used for form a laminoplasty cage according to the presentinvention can vary. Preferably, the body is formed from a rigid,semi-rigid, or flexible radio-lucent material. More preferably, the bodyis formed from materials such as polymers, ceramics, compositematerials, and combinations thereof. Examples of suitable polymersinclude polyether sulfone, polycarbonate, bioabsorbable polymers,polyaryletherketones, and carbon fiber reinforced polymers. The implantcan alternatively, or in addition, be formed from a variety of metals,including titanium, titanium alloys, chrome alloys, and stainless steel.

The marker strip can also be formed from a variety of radiopaquematerials including, for example, metals, polymers, filling salts,ceramics, and combinations thereof. Examples of suitable metals includetitanium, stainless steel, tantalum, cobalt chromium, aluminum, andcombinations thereof. A person having ordinary skill in the art willappreciate that the body can be formed from a radiopaque material, andthe marker strip can be formed from a radio-lucent material.

One of ordinary skill in the art will appreciate further features andadvantages of the invention based on the above-described embodiments.Accordingly, the invention is not to be limited by what has beenparticularly shown and described, except as indicated by the appendedclaims. All publications and references cited herein are expresslyincorporated herein by reference in their entirety.

1. A method for implanting a medical device, comprising: forming atleast one cut in a portion of a vertebra of a patient's spine toseparate the vertebra into at least two halves; and positioning opposedends of an elongate body between two halves of the vertebra to enlarge aspinal canal formed within the vertebra such that a slot-free anteriorside is positioned adjacent to the spinal canal and a plurality ofelongate slots formed in cephalad, caudal, and posterior sides of theelongate body are positioned away from the spinal canal.
 2. The methodof claim 1, wherein a first cut is formed in a spinous process of avertebra of a patient's spine to separate the spinous process into twohalves that seat the elongate body therebetween, and wherein at leastone of a second and third cut is formed on a side of the spinous processbetween the spinous articular process and the transverse process to forma hinge that is effective to allow the two halves of the spinous processto be separated.
 3. The method of claim 2, wherein the elongate body ishollow, and the opposed open ends of the hollow elongate body arepositioned adjacent to the two halves of the spinous process.
 4. Themethod of claim 3, wherein the open ends are angled such that planesdefined by the first and second ends converge.
 5. The method of claim 3,wherein the hollow elongate body has an anatomical cross-sectionextending in a direction transverse to a longitudinal axis extendingbetween the opposed open ends, such that the cross-section of the hollowelongate body conforms to the shape of the two halves of the spinousprocess.
 6. The method of claim 5, wherein the cross-section of thehollow elongate body has a shape selected from the group consisting of aparallelogram, a square, a rectangle, a diamond, an oval, and a circle.7. The method of claim 1, wherein the posterior and anterior sides havea length extending along the longitudinal axis that is greater than alength of the cephalad and caudal sides.
 8. The method of claim 1,wherein each slot extends in a direction transverse to the longitudinalaxis of the elongate body.
 9. The method of claim 8, wherein at leastone of the slots includes a suture-receiving recess formed therein thatis effective to receive and prevent movement of a suture disposed withinthe slot, and wherein the method further comprises the step of passingat least one suture through at least one of the slots such that the atleast one suture is positioned within at least one suture-receivingrecess, and attached the suture to bone adjacent to the hollow elongatemember to anchor the hollow elongate member to the patient's vertebra.10. The method of claim 1, wherein the anterior side of the elongatebody is curved such that an outer surface of the anterior side isconcave.
 11. The method of claim 1, wherein the elongate body is curvedsuch that an outer surface of the anterior side is concave, and an outersurface of an opposed posterior side is convex.
 12. The method of claim1, wherein the elongate body includes first and second halves positionedon opposed sides of a midpoint of the hollow elongate body, the firstand second halves being angled with respect to one another.
 13. A methodfor implanting a medical device, comprising: cutting a spinous processin a patient's vertebra to form a bisected spinous process having twohalves; separating the two halves of the bisected spinous process; andpositioning an elongate body between the two halves of the bisectedspinous process to enlarge a spinal canal formed within the vertebra andto position a spinous process replacement member extending outward fromthe elongate body at a location in which the spinous process replacementmember mimics the spinous process before it is bisected.
 14. The methodof claim 13, wherein the spinous process replacement member has a shapethat conforms to a natural shape of the spinous process.
 15. The methodof claim 13, further comprising the step of attaching muscle separatedfrom the spinous process to the spinous process replacement member. 16.A method for implanting a medical device, comprising: cutting a laminain a patient's vertebra such that a spinous process and a spinousarticular process of the vertebra are separated from one another; andpositioning an elongate body between the separated spinous process andspinous articular process such that a fixation element receiving memberextending outward from a first end of the elongate body is positionedadjacent to the a posterior side of the spinous articular process, andan extension member formed on the elongate body and opposed to thefixation element receiving member is positioned adjacent to an anteriorside of the spinous articular process; passing at least one suturethrough at least one slot formed in the elongate body such that the atleast one suture is positioned within at least one suture-receivingrecess formed in the at least one slot; and attaching the at least onesuture to bone adjacent to the elongate body to anchor the elongate bodyto the vertebra.
 17. The method of claim 16, further comprising the stepof attaching the fixation element receiving member to the spinousarticular process using a fixation element.
 18. The method of claim 17,wherein the fixation element receiving member includes a bore formedtherein, and wherein the fixation element comprises a bone screw, andwherein the step of attaching the fixation element receiving member tothe spinous articular process comprises threading the bone screw throughthe bore and into the spinous articular process.
 19. The method of claim16, wherein the fixation element receiving member and the extensionmember each extend at an angle away from one another with respect to alongitudinal axis of the elongate body that extends between opposedfirst and second ends of the elongate body.
 20. The method of claim 19,wherein the fixation element receiving member extends in a posteriordirection at an angle, relative to the longitudinal axis, in the rangeof about 35° to 75°.
 21. The method of claim 16, wherein a first concaverecess is formed in the first end of the elongate body between thefixation element receiving member and the extension member, and thefirst recess seats a portion of the spinous articular process.
 22. Themethod of claim 21, further comprising a second concave recess formed ina second, opposed end of the elongate body, the second concave recessseating a portion of the cut lamina adjacent to the spinous process.